Laser dimension comparator

ABSTRACT

A nondestructive dimension measuring and comparing system wherein a coherent light beam is impinged on a workpiece surface to produce one or more spots of light. Back-scattered light from the spot or spots is directed onto a vidicon screen to provide at least two light spot image points which are spaced in proportion to a dimension of the workpiece. The vidicon is scanned to provide output pulses which are time spaced in proportion to the image spot spacing. A scaling oscillator provides scaling pulses which are gated to an up-down counter by the electronically processed, time-spaced pulses. Logic circuitry counts and displays the gated scaling pulses to indicate the dimension, or alternatively, compares the count to a reference and displays the deviation.

Cullen et al.

1 1 LASER DIMENSION COMPARATOR [75] Inventors: Donald L. Cullen; Teddy L. Moore,

both of Columbus, Ohio [73] Assignee: Autech Corporation, Columbus,

Ohio

1 1 Notice: The portion of the term of this patent subsequent to Mar. 12, 1991, has been disclaimed.

[22] Filed: Jan. 15, 1973 [211 Appl. No.: 323,786

Related US. Application Data [63] Continuation-in-part f Ser. No. 148,466, June l,

1971, Pat. No. 3,796,492.

[52] US. Cl. 356/1; 356/4; 178/68. [51] Int. Cl. G01c 3/00 [58] Field of Search 356/1, 4, 108; 178/68 [56] References Cited UNITED STATES PATENTS 3,376,836 5/1945 Tunnicliffe 356/1 3,180,205 4/1965 Heppe et a1. 356/1 *July 22, 1975 3,610,754 10/1971 Pirlet 356/1 3,693,143 9/1972 Kennedy 356/] 3,796,492 3/1974 Cullen ct al. 356/4 Primary Examiner-Maynard R. Wilbur Assistant Examiner-S. C. Buczinski [57] ABSTRACT A nondestructive dimension measuring and comparing system wherein a coherent light beam is impinged on a workpiece surface to produce one or more spots of light. Back-scattered light from the spot or spots is directed onto a vidicon screen to provide at least two light spot image points which are spaced in proportion to a dimension of the workpiece. The vidicon is scanned to provide output pulses which are time spaced in proportion to the image spot spacing. A scaling oscillator provides scaling pulses which are gated to an up-down counter by the electronically processed, time-spaced pulses. Logic circuitry counts and displays the gated scaling pulses to indicate the dimension, or alternatively, compares the count to a reference and displays the deviation.

12 Claims, 26 Drawing Figures LASER VIIIIIIIIII/fii 70 PATENTEDJUL22 ms ,895,870

sum 2 FIG. 4 57 LASER VIDTC ON VIIflI/IIIII/li 70 FIG. 5

PATENTEDJUL22 ms 3.895870 SHEET 3 FIG. 6 57 VIDICON FIG? M PATENTEDJUL22 I975 3,895, 870

SHEET 4 I04 06 36 I00 IKHZ I00 KHZ SYNC +|oo HORIZONTAL CLOCK DMDER +|o| SWEEP o OSCILLATOR +|OOK I02 l2 5 I /|4O 4.2 MHZ PULSE Fl PULSE SCALING OSCILLATOR I STRETCH J SHAPING 38 11mm L 50A Q06 {VIDEO} IO v I I I AMP I SCALING /"84 402 M ANALOG GATE CIRCUIT JIIUIIL v AVERAGING RANGE RANGE DIVIDER DISPLAY LIMIT +1000 +|oo CIRCUIT TO FIG.9 FIG, 8

PATENTEDJUL22|915 i 95870 SHEET 5 M'7/ IL //244 LATCH d y} LOGIC IL 1 CLEAR SYNC K /250 249 LOAD 230 252 2 ZERO or 1 56-7 3 0- ZERO ET SYNC 254 swncu wiw-fi OP-DEV COUNTER--\-- DIRECTION CIRCUIT .r\ r\ SIGN 27L STORAGE 270 L P COUNTER U a UP-DOWN P GATE Dom COUNlhH LOPERATING V POINT STORAGE 80 2|? 2l6 DISPLAY STORAGE I FIG. 9

.ma aam PATENTEDJUL 22 ms SHEET /IOO IOOKHZ 3:

FIG. IO

PATENTEDJULZZ ms 3.895870 sum 7 FIG. I2

PATENTED JUL 2 2 ms FIG. IZA

Fl G. BA

FIG. I38

FIG. BC

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SHEET 8 PATENTEDJUL 22 ms SHEET -assaaem SHEET FIG. l5

PATENTEnJuLez I915 3.895870 SHEET 12 604 610 602 BIO SIG 604 668 see FIG. l6

LASER DIMENSION COMPARATOR BACKGROUND OF THE INVENTION This application is a continuation-in-part of copending application Ser. No. 148,466 filed June 1, 1971 under the same title now U.S. Pat. No. 3,796,492.

In manufacturing operations, dimension control is necessary for the proper operation of machines and the cooperation of their parts. Also, attractive improvement in profits can be achieved by better dimension control through the consumption of less material to meet specified dimensions or in a reduction of the quantity of rejects due to dimensions outside of tolerances.

In many industrial operations, a gauging system for use together with a dimension control system must be both noncontacting and continuous. For example, in the rolling of sheet materials, the gauging is continuous to not interrupt the movement of the sheet and noncontacting to avoid interference of the gauging head with the manufacturing operation.

Many types of electro-optical gauging systems have been designed for dimension analysis which in turn are used for dimension control purposes.

One type of optical measuring system utilizes the principle of Michelsons interferrometer. In such a system, a light beam from a laser hits a beam splitter which divides the beam into two parts. One part of the beam is reflected to a reference mirror and then back to the point where the beam is split. The other part of the beam passes directly through the beam splitter to a movable measuring reflector and also is reflected to the same point on the beam splitter. If the light returning from the measuring reflector is out of phase with the light returning from the reference reflector, destructive interference occurs and no light passes to a detector. However, if constructive interference occurs, a signal appears at a detector. If the measuring reflector is displaced by a quarter wave length, the light at the point of interference goes from constructive to destructive interference and the output of the detector goes from a maximum to a minimum. By sensing the number of times the light alternates on and off at the detector, a measurement of the displacement of the measuring mirror from one point to another can be obtained. R. S. Krogstad et al. in U.S. Pat. No. 3,398,287 disclosed a modified form of this system.

A second type of optical system is the null detector system such as disclosed in L. A. Whetter in U.S. Pat. No. 3,548,212. In the null system a laser beam strikes a target surface at a specified angle and the backscattered light is focused on a split photo-cell. In the null position, the photo-cells are equally illuminated. However the target moves, an unbalance in the illumination of the photo-cells is detected and fed to a servo amplitier and driver system which repositions the placement of the laser and detector to a null position. The amount of movement of the laser head assembly is detected and displayed.

D. R. Matthews in U.S. Pat. No. 3,557,380 discloses a modified null system. This patent discloses a transmitter which emits a beam of radiant energy which is directed to irradiate a small area on a surface of a workpiece. A receiver has two detectors with converging respective fields in view disposed on opposite sides of the transmitter. The detectors are directed in such a way that each detector sees the same part of the irradiated area on the workpiece when the workpiece is in the reference position. Thus, in the reference position, the detector signals are equal even though the reflectance on the surface of the workpiece is non-uniform in space distribution. Displacement of the workpiece causes the detector signals to change relative to each other according to a predetermined function and the signals are combined to develop a signal corresponding to displacement.

R. A. Flower in U.S. Pat. No. 3,536,405 discloses an optical thickness gauge utilizing a servo system. This patent discloses a light source which projects a light beam through a rotating prism onto a reflecting mirror. From the mirror, the light is reflected onto a surface of the specimen and from thence to an optical system, diaphragm slit and to a photo detector. The photo detector produces an output pulse each time the beam is scanned across the diaphragm slit. A beam splitter fixed relative to the light source projects a portion of the light beam onto a second mirror mounted on a movable member. The second mirror reflects the light beam onto the opposite surface of the specimen from which it is reflected through an optical system and diaphragm slit onto a photo detector. The second detector produces a second output each time the second beam is scanned across the second diaphragm slit. The times of occurrence of the output pulses are converted to height modulated pulses, the amplitudes of which are proportional to the times of occurrence of the output pulses. Through a servo system, the relative amplitudes are used to position the movable member relative to the fixed member. The displacement of the movable member is indicative of the thickness of the specimen.

R. H. Studebaker discloses, in U.S. Pat. No. 3,437,825, a distance measuring system utilizing laser beam projecting apparatus which projects two laser beams on converging paths from vertically spaced points at a reference location. Vertically spaced and relatively vertically adjustable beam receivers are provided at a second location spaced from the laser beam projector. When the vertical spacing and height of both beam receivers are adjusted so that both beam receivers respectively receive the beams, the elevation of the second location and its distance from the reference location may be precisely determined.

In U.S. Pat. No. 3,541,337, K. Brandenburg discloses a width measuring system which optically scans the width of a sheet by means of a photo-diode and an oscillating prism. A voltage jump is produced at the photo-cell when the light intensity varies on the scan path, for example, at the edges of the sheet. The angular position of the prism at which this voltage jump occurs is determined with the aid of a toothed disk and inductive pickups. Counting the pulses produced by the toothed disk and the cooperating pickups between voltage jumps gives an indication of sheet width.

The optical systems described above, which detect light amplitude or which detect relative light amplitudes, such as the null system, are susceptible to error caused by variations in ambient light conditions, reflectance, and in atmospheric conditions. Systems which depend upon mechanical servo systems are susceptible to error because of the hysteresis which can be expected in a mechanical drive assembly.

There is need, therefore, for a dimension measuring system in which all measurements are objective and do not depend on operator judgments, ambient light conditions. surface reflectance variations, and mechanical limitations.

SUMMARY OF THE INVENTION The invention is a distance measuring apparatus for providing an output correlatable to a distance dimension of a workpiece. The apparatus comprises a coherent light source means for directing coherent light onto said workpiece for inducing backscattered reflections therefrom. A light directing means is positioned for directing said backscattered light from the workpiece. The backscattered light includes at least one relatively large light intensity gradient which has a position related to the distance to be measured. Photoresponsive means is positioned to receive the directed backscattered light for detecting the position of the intensity gradient by providing an instantaneous output proportional to the intensity of the light instantaneously being detected. Scanning means is provided for presenting the reflected light to the photoresponsive means for detection in a time scanning sequence. Signal processing means is connected to receive the output of the photoresponsive means and is responsive to the time period between the scanned detection of the intensity gradients. The signal processing means converts the output from the photoresponsive means to a signal which is correlatable to the distance dimension being measured.

Accordingly. it is an object of the invention to provide an improved laser dimension comparator for measuring the size. shape. and deformation of objects.

Another object of the invention is to provide a laser dimension comparator for continuously measuring the size, shape and deformation of materials such as rubber. plastic. food. glass, paper, textile and metal products.

Another object of the invention is to provide a laser comparator which can be operated accurately by unskilled operators.

Another object of the invention is to provide a laser dimension comparator which reduces the time needed for measuring a dimension.

Another object of the invention is to provide a dimension comparator with a digital display readout which can easily be controlled to read in any system of units desired.

Another object of the invention is to provide a laser dimension comparator having improved construction, maintenance and operation costs.

Further objects and features of the invention will be apparent from the following specification and claims when considered in connection with the accompanying drawings illustrating the preferred embodiment of the invention.

DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates diagrammatically a gauging head constructed according to the invention.

FIG. 2 is a plan view of the workpiece illustrated beneath the gauging head in FIG. 1.

FIG. 2A is a graphical representation ofa pair of high intensity light spots on the workpiece illustrated in FIG. 2.

FIG. 3 is a view in front elevation of the control panel of the data processing console constructed according to the invention.

FIG. 4 is a diagrammatic view of an alternative embodiment of the invention.

FIG. 5 is a diagrammatic view of another alternative embodiment of the invention.

FIG. 6 is a diagrammatic view of an additional alternative embodiment of the invention.

FIG. 7 is a diagrammatic view of a still further alternative embodiment of the invention.

FIG. 8 is a block diagram illustrating a portion of the signal processing circuitry constructed according to the invention.

FIG. 9 is a block diagram of the remaining portion of the signal processing circuitry constructed according to the invention.

FIG. 10 is a schematic diagram of the clock oscillator illustrated in FIG. 8.

FIG. 11 is a schematic diagram of the scaling oscillator illustrated in FIG. 8.

FIG. 12 is a schematic diagram of a portion of the pulse shaping circuit illustrated in FIG. 8.

FIG. 12A is a graphical representation of the signal output from the vidicon illustrated in FIG. 1.

FIG. 13 is a schematic diagram illustrating a portion of the pulse shaping circuitry illustrated in FIG. 8.

FIGS. 13A through 13F are graphical representations of the signals occurring at various positions in the circuitry illustrated in FIG. 8 and FIG. 9.

FIG. 14 is a schematic diagram illustrating the zero set sync switch illustrated in block form in FIG. 9.

FIG. 15 is a schematic diagram of the analog circuit illustrated in block form in FIG. 8.

FIG. 16 shows a series of waveforms illustrating the operation of an improved signal conditioning circuit for the comparator of the present invention.

FIGS. 17A and 17B are detailed diagrams of a signal conditioning circuit which operates in the manner illustrated in FIG. 16.

DETAILED DESCRIPTION The preferred embodiment of the laser dimension comparator described generally has a gauging head and a data processing console. The gauging head is positioned near the object being measured and provides an output signal containing the dimension information. The gauging head utilizes laser optics and image converter electronics. The console, positioned wherever desired, receives and processes the gauging head output signal and generates the ultimate display signal. FIGS. 1 and 2 illustrate the arrangement and operation of the apparatus comprising one embodiment of the gauging head of the present invention. FIG. 1 diagrammatically illustrates a gauging head 10 and schematically its optical interreaction with a workpiece 12. More specifically, the gauging head 10 has a pair of spaced lasers l3 and 14 such as the helium-neon type and cooperating mirrors l6 and 18. The lasers and mirrors function as a coherent light source operative to direct a pair of coherent light beams 20 and 22 onto the target workpiece 12. The coherent light beams 20 and 22 produce a pair of illuminated spots 24 and 26 on the face of the workpiece 12 as illustrated in the plan view of FIG. 2. Although the entire workpiece surface may be partially illuminated. the two light beams 20 and 22 provide points of greatly increased light intensity, such as shown graphically in FIG. 2A. As will be described hereinafter, the distance between these high intensity spots 24 and 26 is directly proportional to the distance from a point on the gauging head 10 to the workpiece I2.

Incident light from the beams and 22 is reflected, not only at an angle equal to the angle of incidence, but in addition, a portion of the incident light is backscattered in all other directions. Some of this backscattered light, illustrated diagrammatically in FIG. 1 as image rays 28 and 30, is backscattered toward a light directing lens 32 mounted in the gauging head 10. A vidicon 34 is positioned in the gauging head 10 relative to the lens 32 to have focused thereon an image of the two high intensity spots 24 and 26. Typically, the lens 32 may have a 50 mm focal length. The distance between the image spots on the vidicon is representative of the actual distance between the spots 24 and 26 on the workpiece l2, and hence directly proportional to the distance from the gauging head 10 to the workpiece 12. A power supply 40 is provided to suitably power the vidicon 34 and the laser power supply 42 which in turn powers the lasers l3 and 14.

In a conventional manner, a voltage having a sawtooth shape generated by a horizontal sweep circuit 36 causes the electron beam of the vidicon 34 to horizontally sweep the vidicon screen. In the preferred embodiment, no vertical sweep is applied to the vidicon 34. Consequently, the vidicon output, after being amplified by a video amplifier 38, comprises a pair of pulses for each horizontal sweep. These pulses, illustrated in FIG. 12A, correspond to the intensity spots 24 and 26 on the workpiece 12 of FIGS. 2 and 2A. The time separation AT between these two video output pulses is directly proportional to the actual spacing between the intensity spots 24 and 26. Therefore, the time spacing AT is directly proportional to the distance from the gauging head 10 to the workpiece 12.

The correlation between the spacing of the intensity dots 24 and 26 and the thickness AD of the workpiece I2 is seen with reference to the geometry of FIG. 1. Examination of FIG. 1 reveals that D: tan Q5 S where D, represents the distance from the cross over point to the surface being gauged and S represents the distance between the spots 24 and 26 on the workpiece 12. Therefore Because tan d) is constant for a fixed installation with the lasers l3 and 14 and the mirrors 16 and 18 rigidly positioned D, KS

where D and D represent the reference surface and gauged surface respectively and where S and S represent the spot spacings of the workpiece surface and the reference surface respectively.

The operation of a vidicon thus provides that the time between the video output pulses, AT, which is directly proportional to the high intensity spot spacing S, is therefore directly proportional to the distance from the cross over point to the gauged surface. The output pulses can then be processed to, in effect, render S D, 0 for the reference surface so that AD S K. Thus, the apparatus illustrated in FIG. 1 produces at its output a pair of time separated pulses in which the time separation is directly correlatable to the workpiece dimension AD.

FIGS. 4 and 5 illustrate a pair of alternative gauging heads to that of FIG. 1, which may be used to provide a pair of spots on an image tube face with a distance therebetween directly proportional to a workpiece dimension.

In the embodiment of FIG. 4, a single laser 50 provides a light beam which impinges upon a beam splitting prism 52 to direct a pair of beams to the mirrors 55 and 56. The mirrors 54 and 56 in turn direct the pair of light beams onto a workpiece 57. A pair of high intensity spots are generated on the workpiece 57 in the same manner as generated by the two lasers illustrated in FIG. 1. A vidicon 58 is provided for detecting this pair of spots in the same manner as illustrated in FIG. 1. The beam splitting prism is of conventional construction.

In FIG. 5, a single laser 60 directs a single beam 62 onto a workpiece to provide a single high intensity spot 63. However, a pair of spaced mirrors 64 and 66 are so positioned to direct backscattered light from the single spot 63 onto prism 69.

The prism 69 is positioned relative to the mirrors 64 and 66 and the vidicon 68 to focus the two-mirrored images of the single spot onto vidicon 68. Thus, in the embodiment of FIG. 5, a pair of high light intensity spot images are generated on the vidicon screen with a spacing directly proportional to a dimension of the workpiece 70; in this instance, the distance from the workpiece 70 to the gauging head 10.

FIGS. 6 and 7 show further modified embodiments or alternative gauging heads with like parts in FIGS. 6 and 7 bearing like reference numerals. The embodiment of FIG. 6 is similar to that shown in FIG. 4 and includes the vidicon 58 with a single laser source 50. In FIG. 6 light is directed in such a way as to produce two spots on the workpiece 57 by means of mirrors 54 and 56. However, in the embodiment of FIG. 6 the prism is replaced by a partially reflecting and a partially transmitting mirror 81 so that preferably half of the coherent light from laser 50 is reflected by mirror 81 onto mirror 56 and the other half of the light from the laser passes through mirror 81 to impinge upon and be reflected by the mirror 54. The embodiment illustrated in FIG. 7 is similar to that shown in FIG. 5 and again involves a single spot 63 on the workpiece 70 produced by a single laser source 60. The embodiment of this figure requires some additional components but has the advantage of producing equal length light paths from the workpiece to the vidicon 68. In addition to the mirrors 64 and 66 for directing backscattered light to the vidicon the gauging head in FIG. 7 is provided with two additional mirrors 83 and 85 for directing light from the offset laser source 60 onto the workpiece at a point coincident with me viewing axis of vidicon 68. In this respect the embodiment of FIG. 7 is similar to that shown in FIG. 1 but utilizes only a single laser source and single spot on the workpiece.

The apparatus illustrated in FIGS. 8 through is the signal processing means 35 connected to the output of the vidicon 34 of FIG. I. The signal processing means 35 is responsive to the time interval between the scanned intensity spots to convert the output from the vidicon to a signal correlatable to a distance dimension of the workpiece. It produces various outputs which are indicative of the measured dimension. These include numerical display, binary coded decimal connections and analog connections.

FIGS. 8 and 9 illustrate. in block schematic diagram. the digital processing network operative to convert the time separation of the vidicon output pulses to a digital readout and visual display of the workpiece position or thickness. The operation of the processing circuitry of FIGS. 8 and 9 is controlled from a control panel illustrated in FIG. 3. The control panel 25 has a digital display 80 for visually reading the desired dimension. In addition, terminals (not shown) are provided for the analog output and BCD output for utilization.

The laser comparator is capable of two modes of operation each controlled from the control panel in FIG. 3. When the gauging head is initially installed for a particular industrial process control, a reference surface at position D (FIG. 1) is positioned a fixed distance from the gauging head 10. In most installations. the position of the reference surface will be on the far side of the cross over point 27 to keep the workpieces away from the gauging head although it can be on the near side. The laser comparator is adjusted (by means explained below) to give a Zero readout when the spots are formed on the reference surface at position D In its first mode of operation, the laser comparator will read the actual thickness AD of a workpiece l2 positioned on the reference surface at D,,. This mode is termed the operating point mode and is herein abbreviated the OP. mode. In an alternative mode of operation, a standard workpiece of known or standard dimension may be positioned on the reference surface in lieu of the workpiece 12. A representative signal of its measured thickness is stored in the storage portion of a comparator circuit. The subsequent output signal from the comparator when a workpiece is measured is a signal deviating from the stored thickness signal in accordance with the deviation of the dimension of the workpiece. For example, a workpiece may be positioned on the reference surface and the button 82 actu ated to put the device in the deviation mode. The zero button 84 is depressed to store the standard dimension of the reference workpiece in the comparator. The digital display 80 will then accurately read the deviation of a workpiece from the standard thickness with a suitable or sign preceding it.

The laser comparator has an operating linear range outside of which the comparator becomes nonlinear. Thus, a workpiece target surface on which the intensity spots are formed must be within a certain distance from the reference surface. An operating range meter 86,

witn its indicating needle 88, provides an analog read out o tlw position of the workpiece surface in or out of the opc rating range. In addition, circuitry is provided to illuminate a signal light on the control panel of FIG. 3 to indicate that the device is operating outside of its or) .rating limits. The crating range is 'nited by the size of the screen of the vidicon 34 and the image reduction. As the workpiece is moved further from the gauging head. the spots become further apart until eventually they will be imaged on the edge of the vidicon screen and eventually off the vidicon screen, thus providing no meaningful reading.

In order to compensate for light and electronic noise and variations, the laser comparator has the capability of averaging the scanned distance between the spots over a time interval of one-tenth of a second, or in the alternative of I second. The averaging time interval is manually selected by the control button 85.

The circuit of FIG. 8 is directed to shaping the pulses from the video amplifier 38 and to converting them into a series of high frequency pulses which can then be counted by the counting and logic circuit of FIG. 9. The circuit is provided with two different oscillators. A clock oscillator is provided to control the logic functions of the circuitry of FIG. 9 and to control the vidicon sweep. The clock oscillator 100 is illustrated in detail in FIG. I0. It is crystal controlled and preferably oscillates at I00 KHz. In other respects, it may be an oscillator of standard design.

The other oscillator is a scaling oscillator 102 which is illustrated in detail in FIG. 11. The scaling oscillator 102 provides high frequency pulses which are to be gated and counted to determine the measured dimension. The preferred scaling oscillator 102 is illustrated in detail in FIG. 11. It too is crystal controlled and operates preferably at a frequency of 4.2 MHZ, for example, so that the readout is in mils. By alternatively substituting a crystal to provide oscillation at 10.6 MHz, for example, the circuit may give a direct readout in meters. Thus. the output scale of the digital display 80, shown in FIG. 3, can be selected by appropriately selecting the crystal frequency of the crystal 103 illustrated in FIG. 11.

Returning to FIG. 8, the output from the clock oscillator 100 is applied to a sync divider 101 which is a frequency divider circuit having three outputs. The first output 104 has the clock oscillator frequency divided by I00 and therefore has a I KHZ output frequency. These 1 KHZ output pulses are referred to as dump pulses. The second output 106 has the clock oscillator frequency divided by ten thousand and therefore has an output frequency of 10 Hz. The third output 108 has the clock oscillator frequency divided by one hundred thousand and therefore has an output frequency of 1 Hz. The divider output terminal 104 is connected to the horizontal sweep circuit 36 to trigger the vidicon sweep at a l KHZ rate. The vidicon therefore sweeps I000 times per second and provides one thousand pairs of output pulses each second which are time separated in proportion to the spacing of the light intensity spots on the workpiece. The divider outputs 106 and 108 are applied to the logic circuitry of FIG. 9 for logic control clock purposes to be described in connection with the description of FIG. 9.

The video amplifier 38 illustrated in FIG. 1 and illustrated in phantom in FIG. 8 receives, at its input, the time separated pulses illustrated in FIG. 12A. The details of video amplifier 38 are illustrated in FIG. 12. The video amplifier 38 includes a vidicon target voltage adjusting potentiometer 120 which compensates for ambient light and target reflection, an amplifier 126, and preliminary pulse shaping circuits in the form of a filter and amplifier stage 128 and a clipping stage 130.

The output from the video amplifier 38 is applied to a video pulse shaping circuitry 140 shown diagrammatically in FIG. 8. The purpose of the pulse shaping circuitry 140 is to provide a single pulse, the width of which is directly and accurately proportional to the distance between the light intensity spots focused on the vidicon screen. The output from the video amplifier 38, which is the input to the video pulse shaping circuitry 140, is illustrated in FIG. 13A. The filter and amplifier stage 128 has removed the noise variations from the signal.

FIG. 13 shows in detail the structure of the first portion of the video pulse shaping circuitry 140. Referring to FIG. 13, the first stage of the pulse shaping circuitry 140 comprises a differentiator 141. The purpose of the differentiator is to differentiate the waveform of FIG. 13A to provide a rapid rate of change for each spot to be used as references for measuring the distance between the light intensity spots. This differentiated output, illustrated in FIG. 13B, is applied to a one shot 143 in FIG. 13. The function of the one shot 143 is to produce a square pulse for each light intensity pulse. The one shot is triggered by the rapid rate of change exhibited at 160 and 170 in FIG. 133. Thus, the one shot output is a pair of successive squared pulses for each vidicon sweep wherein the leading edges of each pulse have a fast rise time and are separated by a time separation which is directly proportional to the distance between the light intensity spots on the workpiece.

The one shot output, illustrated in FIG. 13C, is then applied to a set/reset flip-flop not shown. The set/reset flip-flop produces a single, square, output pulse, the width of which is directly proportional to the distance between the light intensity spots on the workpiece and is illustrated in FIG. 13D. Thus, the first one shot output pulse 176, illustrated in FIG. 13C, causes the set/reset flip-flop to go to its set condition 178 illustrated in FIG. 13D. The second one shot output pulse 180 causes the set/reset flip-flop to go to its reset stage.

Returning now to FIG. 8, the output from the set/reset flip-flop, which is shown in FIG. 8 as the output of the video pulse shaping circuit 140, is, in an alternative embodiment of the invention, applied to pulse stretcher circuit 182 shown in phantom in FIG. 8. However, in the preferred embodiment, the output of the video pulse shaping circuit 140 is applied directly to a scaling gate 184. For purposes of present discussion, the preferred alternative will be considered and the pulse stretching circuit will be discussed below.

The output of the scaling oscillator 102 is also applied to the scaling gate 184. The scaling gate 184 is a gate which is controlled by the square pulses, illustrated in FIG. 13D, from the video pulse shaping circuit 140. These pulses gate the high frequency scaling oscillator pulses which are applied by the scaling oscillator 102. Thus, the leading edge 186 of the output of the pulse shaping circuit 140, illustrated in FIG. 13D, opens the gate to permit passage of the scaling oscillator 102 pulses to the output of the gate 184. The trailing edge 188 of this pulse then closes the gate to prevent passage of further scaling oscillator 102 pulses. In

this manner, the pulse width is converted to a series of pulses capable of being counted. The number of scaling oscillator pulses present at the output of the gate 184 during each burst of such pulses is directly proportional to the spacing between the light intensity spots on the workpiece. It should be noted that a similar burst of such pulses is present at the gate output for each vidicon sweep. In the preferred embodiment, the output of the gate 184 is therefore a series of such pulse bursts occurring at the sweep rate of 1000 bursts per second.

The output of the scaling gate 184 is applied to an averaging divider 190. The averaging divider 190 has a pair of alternatively selectable outputs. The first output 192 divides the scaling oscillator pulses present in each burst by 100. The second output 194 divides the scaling oscillator pulses in each burst by 1000. Thus, if 2000 pulses are present in a burst at the output of the gate 184, then they will produce 20 pulses at the output terminal 192 of the divider 190 and two pulses at the output terminal 194 of the divider 190.

The input to the averaging divider 190 is illustrated diagrammatically in FIG. 13F. These output pulses, together with the sync divider outputs from terminals 106 and 108 in FIG. 8, are then applied to the logic circuitry illustrated in FIG. 9.

The purpose of the logic circuitry in FIG. 9 is to convert the pulse bursts from the output of the averaging divider 190 to a digital display of the distance AD of FIG. 1. The number of pulses at the output of the averaging divider 190 is directly proportional, as stated above, to the distance between the light intensity spots and therefore is correlatable to the distance AD and is directly proportional to the distance from the gauged surface to the cross over point.

A selected one of the two alternatively selectable clock pulses at the outputs 106 and 108 from the sync divider 101 is applied to a logic sync circuit 200 illustrated in block form in FIG. 9. The function of the logic sync circuitry 200 is to provide a sequence of three different output pulses to three different circuits for each pulse input from the sync divider 101. Thus, if the 1 Hz clock pulse at terminal 106 is applied to the sync circuitry 200, then a three-pulse sequence of control pulses will appear at the output of the sync circuitry 200 each second. If the 10 Hz clock pulse output 108 is applied to the sync circuitry 200, then 10 three-pulse sequences occur at the output of the sync circuitry 200 each second. The sequence of three control pulses occurs immediately after the clock pulse from the sync divider 101. The three pulses are of short duration, for example of IO microseconds each, in the preferred embodiment. All three occur before any substantial sweep of the vidicon has occurred, and therefore all three occur before any pulse bursts appear at the output of the averaging divider 190 of FIG. 8. The function of these three control pulses will be discussed below.

The output bursts from the averaging divider 190 of FIG. 8 are applied to a double pole, double throw switch 206. The divider 190 output which is selected by the switch 206 is applied to a counter gate 210. The counter gate output is in turn applied to an up-down counter 212.

The up-down counter 212 is a binary counter which is capable of counting either up or down. Thus, it can add each incoming pulse to the accumulated total number of pulses or it can subtract each pulse from the previous numerical state. The counter gate 210 steers the 

1. A laser dimension comparator for providing an electrical output indicative of a distance dimension of a workpiece comprising a laser light source for directing a single beam of coherent light onto a workpiece to produce a single laser light intensity gradient on the surface of said workpiece, a photo detector positioned adjacent said source, a pair of light directors on opposite sides of said beam for forming a pair of spaced backscatter light intensity gradients on the face of said photo detector from the gradient on said workpiece, and an electrical circuit coupled to said photo detector for producing an electrical output signal indicative of the position of said images on the face of said photo detector.
 2. Apparatus according to claim 1 wherein said electrical circuit includes means for producing a signal indicative of the distance between said images.
 3. Apparatus according to claim 2 wherein said signal is indicative of the distance between the centers of said images.
 4. Apparatus according to claim 3 wherein said beam passes directly from said laser light source to said workpiece.
 5. Apparatus according to claim 1 including at least one additional light director between said laser light source and the workpiece for directing said beam from said light source onto the surface of said workpiece.
 6. Apparatus according to claim 5 wherein said beam is directed by said additional light director substantially perpendicularly onto said workpiece.
 7. A laser dimension comparator for providing an electrical output indicative of a distance dimension of a workpiece comprising a laser light source for directing coherent light onto a workpiece to produce at least one laser light intensity gradient on said workpiece, a photodetector positioned adjacent said source for receiving at least one back scattered laser light intensity gradient image from said workpiece, scanning means coupled to said photodetector for scanning the face of said photodetector and developing an electrical pulse signal indicative of the position of said image on said photodetector, said laser light source comprising means for directing a single beam of coherent light onto said workpiece, an optical means adjacent said photodetector for developing a pair of backscatter images on said photodetector from the light intensity gradient of said single beam on said workpiece.
 8. A laser dimension comparator according to claim 7 wherein said optical means comprises a pair of light reflectors on opposite sides of said single beam of coherent light.
 9. A laser dimension comparator according to claim 7 comprising storage means coupled to said scanning means for storing a signal indicative of the position of a first image on said photodetector, and a signal comparator coupled to both said scanning means and said storage means for comparing said first image signal with a second signal from said scanning means indicative of the position of a second image on said photodetector.
 10. A laser dimension comparator according to claim 9 including a digital display coupled to the output of said signal comparator.
 11. A laser dimension comparator according to claim 10 wherein said signal comparator comprises an up-down counter.
 12. A laser dimension comparator according to claim 11 wherein said storage means comprises a display storage coupled between the output of said up-down counter and said digital display, and an operating point storage coupled between the output of said diSplay storage and the input of said up-down counter. 